Many applications for video coding currently exist, including applications for transmission and storage of video data. Many video coding standards have also been developed and others are currently in development. Recent developments in video coding standardisation have led to the formation of a group called the “Joint Collaborative Team on Video Coding” (JCT-VC). The Joint Collaborative Team on Video Coding (JCT-VC) includes members of Study Group 16, Question 6 (SG16/Q6) of the Telecommunication Standardisation Sector (ITU-T) of the International Telecommunication Union (ITU), known as the Video Coding Experts Group (VCEG), and members of the International Organisations for Standardisation/International Electrotechnical Commission Joint Technical Committee 1/Subcommittee 29/Working Group 11 (ISO/IEC JTC1/SC29/WG11), also known as the Moving Picture Experts Group (MPEG).
The Joint Collaborative Team on Video Coding (JCT-VC) has the goal of producing a new video coding standard to significantly outperform a presently existing video coding standard, known as “H.264/MPEG-4 AVC”. The H.264/MPEG-4 AVC standard is itself a large improvement on previous video coding standards, such as MPEG-4 and ITU-T H.263. The new video coding standard under development has been named “high efficiency video coding (HEVC)”. The Joint Collaborative Team on Video Coding JCT-VC is also considering implementation challenges arising from technology proposed for high efficiency video coding (HEVC) that create difficulties when scaling implementations of the standard to operate at high resolutions in real-time or high frame rates.
Video data is represented in one of several ‘chroma formats’, which specify the sample aspect ratio between a luma and multiple chroma channels of the video data. The aspect ratio implies a fixed relationship between collocated block sizes for luma and chroma for each chroma format. The fixed relationships also affect the available transform sizes used for the luma channel and chroma channels of a collocated block. When video data is represented using a “4:2:2” chroma format, a non-square relationship exists between the luma samples and the chroma samples. A consequence of this is that for a square block of luma samples, the collocated block of chroma samples will be rectangular in shape. Square transforms are normally used for the luma channel and desirably, square transforms are also used for the chroma channels. Transform boundaries may introduce visible artefacts into compressed video data, reducing the perceived quality of the frame. These artefacts tend to be visible along transform block boundaries, especially at low quality levels (i.e. at higher compression ratio or low bit-rates). One approach to removing, or minimising, the perceived impact of these artefacts is to use a ‘de-blocking filter’ to smooth discontinuities introduced at the transform boundaries.